1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and, more particularly, to an improvement in active matrix substrate employed in such an apparatus.
2. Description of the Related Art
A liquid crystal display apparatus or device has been generally used in various fields such as office automation equipment, car-mounted equipment and measuring instruments, since the device has a feature of less consuming electric power and space saving. Among all, an active matrix type device has attracted attention as a display means capable of full color display and realizing high contrast and high refinement.
The active matrix type liquid crystal display device includes an active matrix substrate provided with a plurality of pixels each having a switching element such as a thin film transistor. It is necessary to connect the substrate to a driver integrate circuit (IC). While various kinds of connection structures have been proposed, such a structure is generally employed that connecting terminals on the substrate are bonded by way of an anisotropic conductive film (ACF) to a tape-carrier package (TCP) having the driver IC.
In such a structure, the terminal portion for connection is made of a metal wiring layer covered with a chemically stable transparent conductive film, and a part of the transparent conductive film is attached or bonded to the anisotropic conductive film. The portion of the conductor portion of the terminal not bonded with the anisotropic conductive film is used as a checking terminal to check the electrical connection between the terminal of the tape-carrier package. That is, a measuring probe is applied to the conductor portion so as to check whether or not the tape-carrier package and the terminal are electrically connected.
Since the transparent conductive film covering the metal wiring is composed of a metal oxide, it cannot be formed thick in view of insuring transparency, so that there may exist some pin-holes in the transparent conductive film. For this reason, the metal wiring is subject to an atmosphere through the pin-poles, so that there occurs corrosion on the wiring. Further, even if there is no defect, the metal wiring also suffers from corrosion due to moisture permeating the transparent conductive film in a high temperature and high humidity atmosphere. As the corrosion proceeds, the wiring is disconnected or broken out finally.
As a countermeasure against the moisture, the exposed portion at the terminal portion is considered to be covered with a silicone resin thereby providing shield from the external moisture. Although this can suppress corrosion in the metal wiring, it requires an additional step of coating the silicone resin resulting in increase in cost. Alternatively, the terminal portion of the active matrix substrate may be completely covered with the anisotropic conductive film. In this case, the corrosion of the wiring can be suppressed even without coating the silicone resin. However, this results in a disadvantage that checking the connection between the carrier package and terminal portion is impossible because the measuring probe can not be applied to the conductor portion of the terminal portion.